Dermot Flynn, Director, Strategic Marketing, Medical – Advanced Energy
In the world of manufacturing, a critical system failure creates real-world impacts such as lost productivity, as well as cost for repairs and service to resolve the problem. In the field of medical equipment, system downtime not only incurs costs but also causes delays to patient care that can directly impact patient health.
While having a slick field service operation to rapidly address field failures is essential, it would be better if failures could be predicted. This way, steps can be taken to address the problem before downtime occurs.
With the size and weight constraints put on many modern designs, there is little, if any, space to add sophisticated monitoring systems that would enable failure prediction. However, selecting an intelligent power solution that offers digital monitoring and control can provide an insight into system health that supports failure prediction without requiring additional design, space or cost.
The Consequences of Failure
Whether it is an MRI scanner or a surgical laser system, the majority of capital medical equipment will be backed up by a service contract with defined response and repair times. In an ideal situation, the machine will be located close to the engineering resource, but it could also be deployed in a remote location that is difficult and expensive to reach quickly. Aside from the loss of a critical and often limited medical capability, there will be hard costs that may include expensive long-distance travel and overtime for service staff and intangible costs such as loss of reputation with the customer. Simply put, nothing good happens as a result of an unexpected field failure.
Now imagine a scenario where the customer equipment is monitored remotely and where subtle changes in behavior that may be indicative of future failure can be identified even before an on-site the operator has a chance to see them. In such a scenario, engineers can be dispatched ahead of any system failure with advanced knowledge of what they are looking for. The potential for downtime is therefore reduced.
This is the world of preventative maintenance and monitoring. It is relatively rare that sudden failures happen without any warning if you know where to look or listen. For example, a worn bearing in a fan or other mechanism will produce more audible noise and may have more resistance to turning. A capacitor that is failing may lead to more ripple and noise on the supply line. These are just examples and a good failure modes and effects analysis (FMEA) can provide service engineers with a roadmap as to what changes in equipment behavior could mean.
Given the benefits of anticipating failures before they happen, increasingly large medical capital equipment now includes monitoring specifically intended to ‘keep an eye’ on areas of the design that may be subject to wear or premature failure. This can include devices such as temperature sensors to monitor additional heat generated from friction or even strategically placed microphones that listen for the change in sound from a mechanism that is wearing.
The monitoring becomes all the more powerful and valuable if it can be monitored remotely, either at the customer site or, ideally, in the equipment supplier’s service department – generating a notification if pre-set limits are exceeded.
Unfortunately, every additional sensor adds cost and complexity – for the sensor itself as well as the signal processing circuitry. And even if the cost is not prohibitive, in densely packed machines the required space may simply not be available.
However, there is an alternative way of checking on system health. In many cases, especially in electro-mechanical systems, impending failure often results in greater current draw from the power source as more energy is required to overcome increasing friction. By monitoring the output rails of the power system within large capital equipment, it is possible to provide extensive coverage of many areas that may be subject to early wear-out and to gain insight into potential failure conditions.
Using PMBus™ to Implement a Comprehensive Monitoring System
With almost all power solutions being sourced as complete sub-assemblies from specialist manufacturers, the ability to monitor has to be designed into the power supply from the start. Fortunately, many high-quality power solutions now include technology that allows the power supply to be configured, controlled and monitored.
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Figure 2: PMBus allows configuration, control and monitoring of power systems
Considered by many to be one of the most significant advances in power supply intelligence is the Power Management Bus – or PMBus. This standard as a means of communicating with a power supply over a digital communication bus was developed by several leading power supply manufacturers including founding member Artesyn Technologies (now part of Advanced Energy).
PMBus is an open standard, owned by the System Management Interface Forum (SM-IF) and it is royalty-free with released specifications freely available. These specifications cover all aspects of the requirements including transport and command language. While other standards such as I2C exist, there are shortcomings and, although PMBus is electrically compatible with I2C, it offers more features and overcomes the noise-related (and other) issues often associated with I2C.
The PMBus command language is both extensive and comprehensive, and every value that can be written can also be read, making for a comprehensive monitoring capability for power. Examples of parameters that can be read include output voltage and power, duty cycle, switching frequency and current sensing / scaling and calibration. Typically, the host device will constantly poll all PMBus devices although, in the event of a fault an individual PMBus device can alert the host immediately via an interrupt.
A PMBus-Capable Power Solution
Advanced Energy’s Excelsys CoolX power supplies offer a PMBus-capable modular solution for industrial applications and are available in versions qualified for medical use. The CoolX chassis accepts up to six CoolMod modules, allowing for up to 12 isolated DC outputs ranging from 2.5 to 58 V to be added. A total of 12 different CoolMod modules are available, giving huge flexibility to configure sophisticated power schemes with minimal design effort.
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Figure 3: Advanced Energy’s CoolXÒoffers PMBus capability and modularity
Operation without a fan is possible due to efficiency levels that approach 93%. This enhances reliability, giving a mean time between failures (MTBF) of >2,900,000 hours and a 5-year warranty. It also completely eliminates vibration and acoustic noise.
All CoolX modular power supplies fully implement PMBus functionality allowing full power supply monitoring to be implemented as part of a preventative maintenance scheme. Furthermore, the modular design means that, if there is any failure within the power supply, then servicing is far simpler than with a traditional power solution. In fact, replacement of the chassis or individual modules requires little more than a screwdriver. As there is a limited number of chassis and modules, service engineers or customers can keep spares with relatively little effort and investment, ensuring that downtime is kept to an absolute minimum.
Implementing a preventative maintenance program using technology to monitor for the tell-tale signs of change that often occur before a failure can eliminate downtime. This approach ensures vital equipment remains available and servicing costs are kept as low as possible. Because changes in power consumption are often a good indicator that something is afoot, modern control and monitoring solutions such as PMBus are invaluable in identifying and reporting potential failure conditions so that appropriate action can be taken before a breakdown occurs. Advanced Energy’s CoolX series of modular power supplies implement PMBus, allowing them to be used at the heart of a preventative maintenance system. These advanced power solutions are fully modular which means that service or replacement is simple and quick, requiring few skills or tools.